I'm getting the Creative Cloud subscription in two weeks and two things I want to know is:

A. I created a 30 second rendered composition that I'd like to use to promote my friend's new soulful album on YouTube/Facebook/etc.. using the 30-day free trial of After Effects CC. I figure Adobe would have the capability to watermark such compositions, so I don't want to get into any legal trouble. Can created commercial like the one I just mentioned content be used based off the 30-day free trial software?

B. If it can't, when I pay in two weeks for the AE Creative Cloud Subscription, can I use that same project if I re-render it? Is there any technical watermark issues from transfering a composition from the 30-day free trial version to the paid-subscription version?

There are no watermarks nor any other limitations. Adobe has no control over your content. Not technically, not legally. If at all this would only be relevant for using specific content such as it is available in the CC Libraries, but as a trial user, you only have access to free content, anyway.